Frequency multiplier and wave signal generator



G. WADE June 18; 1963 FREQUENCY MULTIPLIER AND WAVE SIGNAL GENERATOR L|.l: (n

Filed Oct. 1, 1959 IIVVENTOR G Zen Wade O moEmwzmw 22m mozwmmumm Un wd Sa es P ten 3,094,643 L FREQUENCY MULTWLIER AND WAVE SIGNAL GENERATORGlen Wade, Menlo Park, Calif., assignorto Zenith Radio Corporation, acorporation of Delaware Filed Octal, 1959, Ser. No. 843,663 2 Claims.(Cl. 315-3) V The. present invention is directed to a frequencymultiplierandsi'gnal generator for developing millimeter, waves. Itstemsfrorn research conducted on beam-type. transvers rnode parametricamplifiers and employs both structures and operating principlesdeveloped for such amplifiers. U

In:a bea;m type transverse-mode parametric amplifier, abeam is projectedalong a path to a collector and a condition of electron resonance isestablished in, the beam. That condition may onveniently be achievedbyasolenoid arranged coaxially of the beam path and havinga selected 110.energization which provides a magnetic field cgrresponding to a desiredelectron or cyclotron resonance. A coupler to which an input signal is.applied effects deflection modulationof the electrons of the beam tothe end that the electrons are placed into .orbital motion, that is,they arecaused to travel helical paths.- In this fashion, an electronwave representing the signal applied to the coupler is developed on thebeam as it passes through the field of,that coupler; v

I he radius of the orbit 1 paths reflects theinstantaneous amplitude ofthe signal and, accordingly, to amplify the electron wave representingthat signal it is necessary to increase the radius of orbital movement.Such increase in orbital motion is accomplished by what. is referred toas a modulation expander. Inone practical and effective form, themodulation expander is a quadrupole electrode structure which develops anon-homogeneous field that is symmetrical with respect to the beam path.The energy for this field, which is also the energy required foramplification, is delivered by a pump signal generator which, in onespecific form of transverse-mode amplifier, has an operating frequencyof approximately twice the cyclotron frequency. Such an expander isspecifically described and claimedin a copending application, Serial No.747,764, filed in the name of Glen Wade and assigned to the assignee ofthe present invention.

Another form of modulation expandenjdiifering from the quadrupole typein that it is a DC. structure, is the subject of still anotherapplication Serial No. 840,336 filed September 16, 1959, likewise filedin the name of Glen -Wade and assigned to the assignee of the presentinvention. it is a structure which, While energized by aD.C-.-potential,- simulates a-pumping field which appears to theelectrons of the beamto be rotating in synchronism with these electronsas required to increase the radius of theirorbital motion. a I

As thus far described much of the parametric-amplifier structureis alsoemployedin themillimeter-wave generator of this invention which takesadvantage of the fact that a. multi-polar structure disposed in couplingrelation to the beam, near the final portion of its travel, mayaccomplish frequency multiplication of the electron signal wave conveyedby the beam, Such a generator may supplya load inasmuch as the energyfor driving a load maybe derived through themodulation expander anditsdriving or pump energy source. Consequently, the .arrangementcomprehends a system which maybe characterized as a power source formillimeter .waves.

lt is accordingly an object of the invention toprovide a novel frequencymultiplier and signal generator for producing millimeter waves.

It is a specific object of the invention to provide such 2 frequencymultiplication and such signal. generation premised uponcertainoper-ating principles which are characteristic of a beam typetransverse-mode parametric amplifier.,--.

It-is still another specific object of the invention to provide a novelmillimeterrwave signal generator which, in effect, develops the desiredsignal waves by effecting frequency .multiplicationaof. the. reference,wave signal. 1

.A frequency multiplier andwave signal generator, embodying thesubjectinvention, comprises means for projecting an electron stream .along agiven path and for establishing inthat stream orbital electron motionhaving a rotational component of a-predetennined frequency. Amulti-polar structure is positioned coaxially. of the path and includesatleast two pairs of poles arranged symmetrically about the path incoupling relation to the stream...v There are means forderiving from themultipolar structure an output signal of N times'the aforesaidpredetermined frequency, where N is the number of pairs of polesincluded in the multi-polar structure.

In accordance with. the invention, a modulation expander is positionedalong, the beam path following an input couplernthrough which theelectron stream. passes and as a consequence of which its electrons arecaused to travel orbital paths. .Theexpander is of the DC. type,simulating a pumping ,field which appears to the electronsof the streamto be rotating in synchronism with electron motion. t

The features of. the present invention which are believed to be novelare set forth with particularity in the appended claims. Theorganization and-manner of operation of the invention, togetherwithfurther objects and advantages thereof,-may best be understood byreference to the followingdescription taken in connection with theaccompanying drawings, in the several figures. of which like referencenumerals identify like elements, and in which: Y

-FIGURE 1 is ,a schematic representation one form of a millimeter-wavegenerator; 1

FIGURES. 2 and. 3 representaform of DC. modulation expander which vmayinaccordance. with the invention be employed in place ,ofthe quadrupole orAC. modulation I expander included in the arrangement of FIGURE I; and,v

.-FIGURE 4 is an endview of a modified form of multipolar structure thatmay .be substituted for the multi-polar output coupler ofFIGURE 1.

The arrangement of FIGURE 1,. aside from the multipolar couplingstructure to be described hereinafter, is similar to. the structuredescribed and claimed in the aforementioned Wade application Serial -No.747,764. Reference may be :had to that application for structuraldetailsof the .overall arrangemennincluding provisions for mounting itscomponent parts other than signal sources within a tube envelope, andfor a comprehensive explanation of the, operating principles of themodulation expandenemployed. to increase the amplitude of the electronorbits. These matters will, therefore, be treated in less detail inthisdescription. A I v The arrangement under consideration comprisesmeans for projecting anelectron stream along a given path'l0 and forestablishing in that stream orbital electron motion having a rotationalcomponent of a predetermined frequency More particularly, this-meansis-comprised of the .followingprincipal components: an electron gun forprojecting a stream of electrons, a field arrangement for establishingelectron resonance in Tthe stream,- and a .deflectionmodulator or inputcoupler for developing an electron wave onthe beam-representingareference signalof a predetermined frequency. These components will beconsidered seriatims v r a The electron gun 11 may be entirelyconventional and preferably includes the usual indirectly heated cathodetogether with suitable focusing and accelerating electrodes fordeveloping a well-defined beam or stream of electrons directed alongpath 10. For best operation the beam diameter should not exceed thedimension, measured in a circumferential direction, of the elementalelectrodes constituting a multi-polar output coupler to be describedhereinafter. The electrons travel this path toward a collector or anode12 disposed transversely of the path and maintained at a suitablepositive potential as indicated by the symbol +B.

This means for creating a condition of electron resonance in the beammay be of the magnetic or electrostatic type and, for convenience, isrepresented as a solenoid 14 surrounding the beam path to establishlines of magnetic flux parallel thereto. The solenoid is physicallypositioned externally of the tube envelope and is energized by a DOsource (not shown) of adjustable magnitude for the purpose ofestablishing a desired cyclotron frequency which may be assumed tocorrespond to the frequency of the reference signal to be consideredpresently. In axial length, solenoid 14 is long enough to encompass adeflection modulator or input coupler, a modulation expander and amulti-polar output structure which are disposed in the recited orderalong path as will be made clear hereinafter. The focusing fieldestablished by the solenoid is designated symbolically by arrow H.

The deflection modulator or input coupler may take any of a variety offorms; it may for example comprise resonant cavities, transmission linesor deflection plates spaced alongside the beam for interactiontherewith. As illustrated, the deflection modulator 15 includes a pairof deflector plates 16, 17 located on opposite sides of the beam path. Areference signal generator 18 is coupled to the modulator by means of atransmission line 19 which is short-circuited at one end and is coupledat its opposite end to deflectors 16, 17. A transmission link 21 istapped as indicated onto transmission line 19 in a position adjusted tomatch [the impedance of generator 18 to that presented by the pair ofdeflectors. Transmission line 19 has an effective electrical length ofone quarter wave length at the frequency of the reference signalsupplied by generator 18.

Following deflection modulator 15 in the direction of collector 12 is amodulation expander for expanding the radius of the orbiting electronsto the end that the beam, in effect, sweeps a cylindrical path of suchradius in relation to that of the multi-polar output structure as toattain a substantial coupling therebetween. This modulation expander isof the quadrupole type described and claimed in Wade application SerialNo. 747,764. I-t comprises four electrodes 21, 22, 23, 24 symmetricallydisposed circumferentially around beam path 10. Each electrode has theshape of an equilateral hyperbola and the electrodes are disposed withtheir intermediate portions facing the beam path and their terminalportions projecting outwardly therefrom with each terminal portionspaced generally parallel from the adjacent terminal portions of theneighboring electrodes. Oppositely disposed electrodes 21, 23 arecoupled to one terminal of an alternating-current pump signal generatorand the other pair of oppositely-spaced electrodes 22, 24 are coupled tothe remaining terminal of generator 25. The operating frequency of pumpgenerator 25 is approximately twice that of reference signal generator18.

Positioned coaxially of beam path 10 beyond modulation expander 20 is amulti-polar output structure including a plurality of pairs of polesarranged symmetrically of path 10 for coupling relation to the electronstream. More specifically, this structure has an even number of polepieces with the even-numbered ones interconnected and with theodd-numbered ones likewise interconnected so that the structure isrestricted in excitation to the 1r mode. It is convenient inconstructing the multi-polar device to make use of a pair of iterativecombv11 into the held of input coupler 15.

type conductive structures bent into an annulus and posi' tioned so thatthe tines or electrode element of each such structure interlace withthose of the other. The common band of one such structure is designated31 and it sup ports odd-numbered electrode elements 33, 35, etc. Theband for the companion structure is designated 32; it supports theeven-numbered electrode elements such as 34 and 36. An inductor 40 iscoupled across conductive bands 31, 32 and is tuned by a capacitance 41to constitute a circuit resonant at the output frequency of thegenerator. Capacitor 41 is represented in broken-line construction sinceit may be constituted in whole or in part by the capacitance representedby the interlaced electrode structures comprising elements 31-36. Whilethe lengths of the electrode elements are not critical, they preferablyshould be short compared to one-half the wave length of the outputsignal so that the interlaced structure represents predominantly acapacitance for resonating with inductor 40. Preferably, the internaldiameter of the cylinder defined by interlaced electrode elements 33-36is only slightly larger than the diameter of the cylinder enclosing ordefined by the electron orbits of the beam as it emerges from modulationexpander 20.

A load 42 to which the signal generated by the device may be applied iscoupled to multi-polar structure 30 through an impedance-matchingarrangement similar to that employed in coupling reference signalgenerator 18 to deflection modulator 15.

The potential sources designated E E and E coupled respectively todeflection modulator 15, modulation expander 20 and multi-polarstructure 30 through choices, are sources of unidirectional potentialemployed to determine the drift velocity of electrons along beam path 10and through modulation expander 20. It is practicable to have sources Eand E of approximately equal values and slightly larger than source EThe generator is housed in an evacuated envelope representedsymbolically at 45. Techniques generally similar to those of copendingapplication Serial No. 747,764, may be employed in securing thecomponents of the structure within that envelope.

In the operation of the described millimeter-wave generator, a beam isprojected along path 10 by electron gun As the beam traverses thecoupler, it is subjected to deflection modulation because of theinteraction of the beam with defiectors 16, 17. This deflectionmodulation causes the electrons of the beam to travel along orbitalpaths at the frequency of cyclotron resonance established by magneticfield H; for the illustrated case using simple lumped input couplerelectrodes, the orbital frequency also corresponds to that of thereference signal supplied from generator 18 to the input coupler. Theradius of the electron orbits is determined by the amplitude of thereference signal and for the case under consideration is small comparedto the internal radius of multi-polar output coupler 30.

As the beam enters modulation expander 20, the electrons are subjectedto'a non-homogeneous pumping field which, as explained in copendingapplication Serial No.

747,764, causes a net increase in the radius of the electron orbits, theenergy required for increasing the electron motion being supplied bypump signal generator 25. The drift velocity, which is determined by theapplied operating potentials as noted above, and the axial length of theexpander are so chosen that the radius of the electron orbits as thebeam emerges from the modulation expander is nearly equal to theinternal radius of output coupler 30. In other words, the beam which hasbeen deflected off axis 10 in its passage through input coupler 15rotates about that axis at a radius approaching that of the outputcoupler. Moreover, the electrons of the beam experience a phase-focusingeffect as ff c exhibited byt c .expa riert ndsi o ad ce o remm 95 lec no lt e be m wh n rin antintermediate phase condition causing them toshift toward the nearest optimum phasecondition in which their electronorbits are increased to a maximum. As a result of this phase-focusing orbunching effect, the beam crosssection is distorted from its originalcylindrical shape, the electrons tending'to bunch about the position ofoptimum phase.

As the beam enters output coupler 30 rotating at the frequency of thereference signal from generator 18, it induces in this structure bymeans of space charge coupling effects a signal having a frequency of Ntimes the frequency of the reference signal, where N is the number ofpairs of poles in that structure. In other words, there is amultiplication of the input frequency by a factor corresponding to thepairs of poles in the output coupler which facilitates the generation ofmillimeter waves. The coupling from structure 30 to load 32. constitutesmeans for deriving and for supplying to the load an output signalharmonically related by the factor N to the reference frequency ofsource 1 8.

One restriction of the arrangement of FIGURE 1 is the need of a pumpcapable of supplying a signal of approximately twice the frequency ofthe reference signal delivered by generator 18 or at least of twice thecyclotron frequency. This restriction may be overcome by the use of aDC. modulation expander such as that represented in FIGURES 2. and 3.This structure is the subject of copending application Serial No.840,336. In this case the modulation expander is a multi-filararrangement of helical conductors. As represented, it includes fourconductors 50, 51, 52 and 53 individually having the configuration of ahelix and collectively interlaced to constitute a quadri-filarstructure. The pitch of each helical conductor corresponds with or ismatched to the pitch of the electron orbits of the beam traveling alongpath 10. This quadri-filar structure is energized from a DC, asdistinguished from an A.C. source. The DC. source is designated 54 andhas one terminal connected to opposed conductors 50, 52 whereas theremaining terminal connects to opposed conductors -1, 53 of thequadri-filar structure.

Obviously, the physical arrangement of conductors 5053 is to be suchthat each is insulated from its neighbors and this may be facilitated asa practical matter by providing the conductors with flanges definingchanneh ways between the conductors, as appears from FIGURE 2, intowhich suitable insulating material (not shown) may be placed. It hasalso been found, as explained in copending application Serial No.840,336, that there is a sufiicient approach to the ideal quadrupolefield if the portions of the four conductors of the quadri-fil'arstructure which face beam path 10 outline a square.

The field established within the modulation expander in response to theDC. "excitation is a symmetrical nonhomogeneous pumping field whichappears to the elec trons of the beam to be rotating in synchronismtherewith. This condition accomplishes expansion of the radius of theelectron orbits and phase focusing in a manner analogous to that of thequadrupole modulation expander of FIGURE 1.

The multi-polar coupling structure 30 may, if desired, be amulti-resonant cavity structure similar to that employed as the anode ofa cavity magnetron. FIGURE 4 is an end view of such a structure having aseries of resonant cavities 60-67. Strapping is resorted to, as inmagnetron practice, to assure operation in only the 11' mode. Strappingis accomplished by a conductor 68 which is conduetively connected to theeven-numbered poles of the structure and by a second conductor 69 whichis conductively connected to the odd-numbered poles. An output may bederived from this multi-cavity structure by means of a coaxialconnection 70 which terminates .ina probe, 71 located in one oftheresonantcavities. The other end oi the coaxialv connector may.leaddirectly to the load. When such ratmultiecavitystructure idem:pioyed, the frequency of the output signal is once again N times thereference .ffequenc'y,".1N is then-umber sf P inc udss .Wil in ness 3%The described arrangements ude a modulatiomexpander in order that asignifica amount of energy may be supplied" at a desiredf-requency. Itthe devices were to be used merely as a signal source as distinguishedfrom a power source, the modulation expanders would be omitted. In sucha case the signal applied to input coupler [15 would need be strongeough to deflect the beam away from axis .10 by a significant amountrelative to the beam radius.

While particular embodiments of the invention have been shown anddescribed, it will be obvious to those skilled in the art that changesand modifications may be made without departing from the invention inits broader aspects, and, therefore, the aim in the appended claims isto cover all such changes and modifications as fall within true spiritand scope of the invention.

1 claim:

1. A frequency multiplier and wave signal generator comprising: meansfor projecting an electron stream along a given path; means tor creatingin said path a field for establishing electron resonance in said stream;means for deflection modulating said stream in accordance with amodulating signal of a predetermined frequency to establish thereinorbital electron motion having a rotational component of saidpredetermined frequency; an electron-motion expander positioned alongsaid path for expanding the radius of the orbital motion of theelectrons of said stream, said expander including a multi-filararrangem-ent of interleaved helical conductors coaxial with said pathand a source of unidirectional excitation potential connected acrossadjacent ones of said conductors for simulating within said expander asymmetrical, nonhomogeneous pumping field which appears to be rotatingin synchronism with the electrons of said stream; a multipolar structurepositioned coaxially of said path beyond said expander and including atleast two pairs of poles arranged symmetrically about said path inelectrostatic coupling relation to said stream; and means for derivingfrom said multi pol-ar structure an output signal of N times saidpredetermined frequency, where N is the number of pairs of polesincluded in said multi-polar structure.

2. A wave signal generator comprising means for projecting an electronstream along a given path; means for creating in said path a field fiorestablishing electron resonance in said stream; means for deflectionmodulating said stream in accordance with a modulating signal of apredetermined frequency to impart motion to electrons in said streamalong a helical path of a predetermined pitch related to the strength ofsaid field and with a radius representing the amplitude of saidmodulating signal; an electron-motion expander positioned along saidgiven path for expanding the radius of the orbital motion of theelectrons of said stream, said expander including means for subjectingsaid electrons to non-homogeneous pumping field forces, the strength ofwhich vary linearly with distance from said given path which areuni-directional in a time domain, and which define a field pattern witha plurality of pairs of space-opposed poles disposed along interleavedhelicoid-al loci which are coaxial of said helical path, are of the samepitch as and co-di-rectional with said helical path and which have acoaxial length corresponding to at least one convolution of said helicalpath, the even numbered ones of said pairs being of one polarity and theodd numbered pairs being of the other polarity; a multi-polar structurepositioned coaxially of said given path beyond said expander andincluding at least two pairs of poles arranged symmetrically about saidgiven path in electrostatic coupling relation to said stream; and meansfor deriving from said multi-polar 7 structure an output signal of Ntirnes said predetermined 2,169,725 frequency, Where N is the number ofpairs of poles in- 2,638,539 eluded in said multi-polar structure.2,834,908 2,844,753

References Citedin the file of this patent UNITED STATES PATENTS DeVries et a1. Aug. 1, 1939 De Vries et a1 Aug. 1, 1939 Aug. 15, 1939Cuccia May 12, 1953 Kompfuer May 13, 1958 Quate July 22, 1958 OTHERREFERENCES Amide by R. Adler et 211., pp. 1756-1757, Free. of the I.R.E.for Ootober 1958, No. 10, vol. 46.

1. A FREQUENCY MULTIPLIER AND WAVE SIGNAL GENERATOR COMPRISING: MEANSFOR PROJECTING AN ELECTRON STREAM ALONG A GIVEN PATH; MEANS FOR CREATINGIN SAID PATH A FIELD FOR ESTABLISHING ELECTRON RESONANCE IN SAID STREAM;MEANS FOR DEFLECTION MODULATING SAID STREAM IN ACCORDANCE WITH AMODULATING SIGNAL OF A PREDETERMINED FREQUENCY TO ESTABLISH THEREINORBITAL ELECTRON MOTION HAVING A ROTATIONAL COMPONENT OF SAIDPREDETERMINED FREQUENCY; AN ELECTRON-MOTION EXPANDER POSITIONED ALONGSAID PATH FOR EXPANDING THE RADIUS OF THE ORBITAL MOTION OF THEELECTRONS OF SAID STREAM, SAID EXPANDER INCLUDING A MULTI-FILARARRANGEMENT OF INTERLEAVED HELICAL CONDUCTORS COAXIAL WITH SAID PATH ANDA SOURCE OF UNIDIRECTIONAL EXCITATION POTENTIAL CONNECTED ACROSSADJACENT ONES OF SAID CONDUCTORS FOR SIMULATING WITHIN SAID EXPANDER ASYMMETRICAL, NONHOMOGENEOUS PUMPING FIELD WHICH APPEARS TO BE ROTATINGIN SYNCHRONISM WITH THE ELECTRONS OF SAID STREAM; A MULTIPOLAR STRUCTUREPOSITIONED COAXIALLY OF SAID PATH BEYOND SAID EXPANDER AND INCLUDING ATLEAST TWO PAIRS OF POLES ARRANGED SYMMETRICALLY ABOUT SAID PATH INELECTROSTATIC COUPLING RELATION TO SAID STREAM; AND MEANS FOR DERIVINGFROM SAID MULTI-POLAR STRUCTURE AN OUTPUT SIGNAL OF N TIMES SAIDPREDETERMINED FREQUENCY, WHERE N IS THE NUMBER OF PAIRS OF POLESINCLUDED IN SAID MULTI-POLAR STRUCTURE.